In order to detect the presence of a railway vehicle on a track section, it is a well-known method to use axle counters. The axle counters use detection points installed at each end of a railway track section to count the passage of train axles. The detection points are physically connected to the rails and to a computer. The computer compares the count from the first end of the track section to the one from the second end of the track section: if these two counts are equal, the computer decides that no railway vehicle is present on that particular track section.
Yet this method is bulky and costly, as it requires installing relatively large detection points in contact with the rails, making it prone to error and subject to meteorological conditions. This method could be further impacted by magnetic interferences.
Another method of detecting trains on the track section consists of using track circuits. This method uses insulation joints to insulate track sections. An electric circuit is provided in each track section, and a signal relay detects whether there is an electric current in the track circuit. When a railway vehicle passes, its axle shorts out the electric circuit, and the absence of electric current triggers the signal relay to announce that a railway vehicle is present on this track section.
This method however implies other disadvantages. As it uses electric circuit, a wet weather can hamper its accuracy or even prevent it from detecting trains at all. It is also prone to error from for instance the insulated joint's failure to properly insulate two neighbouring track sections. This method could also be impacted by magnetic interferences.
As an improvement to the above-mentioned methods, it is known to use optical fibres buried right under the railway track for train detection. An example could be found in EP 1 128 171 A1.
Yet this method is not satisfactory either. Indeed, the arrangement of the optical fibre and its related detecting apparatuses is complicated. Moreover, signal processing required to determine whether a railway vehicle is present on the track section is often onerous.